The invention relates to a friction assembly, such as a clutch disk, a brake disk, or similar part. The assembly has a support plate which carries a friction lining and an internal hub which is firmly attached to the hub and is thicker than the support plate.
Friction assemblies are known in which the support plate and hub are part of a one-part thick-walled ring body on which the friction lining is provided. A relatively large thickness of the ring body is required, in such prior art assemblies, because of the surface pressure resulting from the torque transfer in the internal gearing, with which the friction element is usually connected via a shaft.
Knocking, because of vibrations, should be prevented. For clutch disks and brake disks, as used in the construction of heavy machines, there are requirements for low use of material, low moment of inertia, and high carrying capacity. These requirements can be satisfied with a smaller support plate thickness in the area of the friction lining. In addition to a decrease in the rotating masses, the spatial requirements for the friction assembly are also reduced, which is an advantage in cases of use where the available space for construction is small. A thinner support plate also permits, given a certain thickness of the entire friction element, an increase in the thickness of the friction lining and the formation of deeper grooves for leading the oil to the friction linings. This improves the removal of heat and increases the service life of the friction assembly. In general, if thicker friction surfaces are used, the decrease in the thickness of the support plate results in a decrease in the total thickness of the friction assembly.
There exists the possibility of machining a thick unit to cut down the area which supports the friction lining, in order to decrease its thickness in comparison to the hub area. Such a process of manufacturing is, however, very involved and expensive.
German Patent No. OS 2,758,840 discloses a friction assembly in which the support plate and the hub which serve as carriers for the friction lining are separate parts and are interconnected by an unitary joint connection made of these parts themselves. Pins are mentioned which are constructed as an internal part of the hub. The pins grip through openings in the support plate and are plastically deformed, in the manner of a riveted joint, by the application of pressure. In addition, a positive lock of the joining marginal zones of hub and support plate and a joint bonding such as soldering, welding, or glue connection have been suggested.
A rivet joint between a hub and external ring is known from German Patent No. OS 3,436,306, British Patent No. 1,474,964, and U.S. Pat. Nos. 3,300,853 and 4,022,310. As explained in further detail below, tensions are created in the parts to be joined during the riveting, which leads to evenness problems.
The suggested positive locking joint connections between hub and support plate are very involved from the point of view of manufacturing technology. Glue connections are unsatisfactory with regard to carrying capacity and durability. If, because of processing reasons, the connection can only be made after the friction lining has been attached to the support plate, a welded connection cannot be considered because of the thermal stresses involved.
For a rivet joint between hub and support plate, the friction element in the hub zone is made relatively thick. This form cannot always be used because of lack of space. In order to achieve a durable connection for the transfer of torque by means of riveting, a filling ratio as good as possible is required. This ratio in turn can only be achieved if very large forces are used which result in a high degree of flowability in the rivets. As a result, uneven high pressures are generated at some sites in the bores of the support plate, which can lead to undesirable dishing and unevenness of the support plate. As a result, it is difficult to stay within the narrow tolerances which are required in the use of the friction elements as brake disks in, for example, the axle cones of tractors and other all-terrain vehicles. Such brake disks are placed between the brake piston and the stopping disk to convert the kinetic energy of the vehicle which is in motion, either entirely or partially, into heat as a result of friction, when the vehicle is to be stopped or its velocity is to be reduced. Because of the limited force which the driver can apply to activate the pedal, as well as because there exists a maximum pedal travel, there is little room for play. A very small exceeding of thickness tolerances, unevennesses, dishing, and waviness quickly brings the brake disk in contact with neighboring parts. This leads to acceptably high drag torques, premature wearing, and heating of neighboring parts, as well as power loss.
The demand for a construction part which is built with great precision regarding tolerances and shape deviations can be reached in the case of rivet joints of a hub and support plate only if small riveting forces are used. However, this may lead to an unsatisfactory filling ratio with a decrease in supporting surface. Although precision punching can be used to reduce the sum of the additive measurement and position tolerances, the tolerance levels reached in contemporary mass production are insufficient to achieve the desired degree of accuracy by means of riveting. In addition, during braking, high temperatures can occur in the friction element which change the tension situation as generated during the riveting. This, again, can lead to new deformation. The torques which need to be transferred are small. Last, but not least, torque pulses can result in a deformation of the rivets which, because of the machining requirements, are soft.